1. Field of the Invention
The invention relates to a valve having a device for shutting off a valve interior, a cylinder, and a piston guided in the cylinder for positioning the shutoff device and forming a first chamber and a second chamber in the cylinder.
A shutoff valve which is known from Published European Patent Application 0 124 821 A1, corresponding to U.S. Pat. No. 4,607,822, has a piston guided in a first cylinder. The piston is connected to a conical shutoff device through a piston rod guided in a second cylinder. A chamber formed by the bottom of the piston and the bottom of the first cylinder communicates with an annular relief chamber, through a narrow throttle gap and an adjoining wide throttle gap between the piston rod and a wall surface of the second cylinder. Control bores lead from the relief chamber to control valves.
The control valves are opened to close the valve. Pressure medium escapes over the throttle gaps through the control bore provided in the relief chamber. As a result, the piston moves downward. At the same time, the geometry of the throttle gaps changes so that the proportion of the wide throttle gap is reduced in favor of the narrow throttle gap. Accordingly, the damping becomes greater, the farther the second piston is moved into the closing position of the valve. Thus, the conical shutoff device is moved onto its seat counter to an increasing damping force. That reference says nothing else about the function of the valve.
A disadvantage of that valve is that because of its nonlinear damping, it can be used only as a shutoff valve. Moreover, the valve known from the prior art is not suitable for blowing off multiphase mixtures, of the kind that can occur in the primary loop of nuclear power plants that have a pressurized water reactor.